Pro's and cons of displacement upgrades. M96

So I'm in rebuild shopping mode, and I've determined that no matter where I go one of the questions I need to make a decision on is displacement. So whats the thoughts/opinions etc on a 3.6 rebuild. (My 2003 2.6 C4 Cab) stay 3.6, go 3.8 or all the way to 4.0? The thing is its hard to determine the limits of the stock ECU, where is the line where a complete re-tune is mandatory? At what point does more displacement require upgrades to cams heads etc to really get the best bang for the buck? At what point do I start going backwards in reliability? I've pretty much sorted out who to use,, (Not telling yet) I think I have the pricing sorted, looking at a range of about 13K to 23 K depending on shop and parts choices. A couple shops go immediately to the 4.0 since the nickies are about the same price size doesn't matter... A couple say 3.8 is a solid nice improvement, 4.0 doesn't yield as much benefit unless you add parts. So there it is.. let the armchair engine rebuilding commence..

I got a 3.8 and everything else is stock. I had the option to go bigger, but chose not to as it would be wasted on me. I am entirely satisfied with my reconstructed engine. More horsepower and tons more torque, of course, that is not only due to the displacement increase. There are other factors involved in the reconstruction that adds power.

I also went 3.8 with my 3.6 (997 Carrera 4). Research found that you can go about 10% larger without changing the stock ecu programming. So I could have gone 4.0 but I would have been on the ragged edge of what the ECU was expecting, so I elected to go 3.8.

Subscribed. I�m having a 3.6 to 4.0 elective build done later this year. I�ve no doubt the new engine will be a nice upgrade but curious to hear everyone�s experiences.

From my research, bigger isn't always better in the case of the M9X engine. The sweet spot seems to be the 3.8L in terms of power increases and price. What are your intended uses for the engine?

I would go 3.8, along with the components to really make the engine shine. Sometimes going bigger is actually not better. Case in point, I replaced a 350 Chevy with a 400 Chevy, whereas my friend did a 383, but he ended up with stronger cylinder bores, which allowed him to generate more power by spending the money on better heads. But he also gained reliability/durability. My engine started losing oil pressure over time, but his was always tight. EDIT: the Chevy smallblock required siamesed bores to get to 400 cubic inches, which caused the cylinders to oval faster than a 350 or 383 due to lack of cooling in the areas where the cylinders were touching each other. Not saying a 4.0 can�t be done well, but because it�s probably the absolute max for this engine type, it just seems like a sweet spot has more value in the end.

The only possible drawback I can think of 3.6 to 3.8 is larger and heavier pistons might create more in cabin vibration. Most forum members wouldn't care about more engine vibration but the average 996 owner might. And 4.0 with even bigger pistons might be more.

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Hmm...I�d think a good builder would ensure the rods and piston weights are evenly balanced, even more so than factory. Done right, I�d expect the engine to be even smoother than stock.

Jon from EBS Racing here. I've noticed lots of chatter on 3.8 and 4.0 big bore engine builds. We are getting ready to go to dyno with our in house Project 996 3.4-4.0 conversion. For those interested send I can post results and provide details on the rebuild. For questions please contact me at EBS Racing directly [email removed] Thanks Jon

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Is that for street or track? Just wondering.

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Well hello, I am very interested, yes please post the results and the rebuild details.

Yea your(At least I'm) not going to spend the cubic dollars on one of these rebuilds, without balancing on the menu.. Its always been one of the biggest paybacks I've gotten for the money on a rebuild. Absolutely no doubt when you fire up an engine with a solid B&B done to the entire rotating assembly.

Going 4.0. Should be done next week. Requires dyno tuning as there are larger fuel injectors and ECU reflash.

They key to going with a larger bore size (this should be obvious) is to "balance"/blueprint (including rotational balancing) the entire system - this includes Fuel/Air (injectors and air intake), Valve Train/Heads (intake and exhaust porting optimization, valve seats and guides etc.) Pistons/Connecting rods, rod bolts, Chains, Guides, Pin/Weld IMS sprocket, Upgrade IMS Bearing (Dare I say IMS Solution?) Oil pump hex key, etc. etc. etc...The list goes on and on. Last but not least (uh, this is pretty important... ) is the ECU tune to match the new engine dynamics - this takes a real understanding of what went into the construction, and what the upgrades should be able to achieve - it should be done and tweaked by the builder (they should be able to do this in-house and not farm it out to someone else "I've got a really good guy down the block"... - I would think any builder worth their salt would have a dyno in house). There is good reason why it costs A LOT to do this correctly. I find it hard to believe there could be a $10k differential (close to 50% of final price) in two engines that are prepared similarly (i.e. with similar/same parts) and properly (i.e. Labor - if the labor is done carefully/properly, I don't see how there could be more than a 10-15% difference in overall labor cost regardless of rate differential).

Good topic! I have a year to decide what the best option is for me.

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Yes always have the complete reciprocating assembly dynamicly balanced for increased reliability & power.

1- Displacement isn't what dictates where ECU work needs to be employed. We have learned with direct experience that efficiency makes the big difference. As we find more volumetric efficiency each year, we see that more and more engines "need tuning". As we find more efficiency, more power is also made, and unlike what most people believe, the engine will run richer than leaner due to the dynamics associated wit the Bosch DME which is MAF based. Almost everything we built in 2019 was at least 15HP stronger than out was in 2018, and we found that 75% of the engines required a tune to pull fuel under the curve, and then again in the top end. Once we pulled the fuel, the power would be more apparent in both TQ and HP at all RPM points. Put simply, these engines don't "lean out" as they make more power (through efficiency gains) they richen up. The rich condition can wash down cylinder walls, and cause all sorts of issues. Also, as we add displacement, we add bore size, and that usually means that ignition timing must b optimized for the larger bore. Why? Flame propagation. It takes longer for the flame to propagate across a larger bore, and that plays into the efficiency, and enrichment optimization. When tuning we often need to pull fuel, as well was increase ignition timing, which is counterintuitive when it comes to conventional tuning. When you get this right, the engine runs better, performs better, runs smoother, and will have far less chamber contamination. Put simply, we may build a 3.8 from a 3.6, as well as a 4.0 from a 3.6, and the engine that is most efficient is likely the one that will need more tuning to level out the enrichment curve. It is easier to build a more efficient 3.8, than a 4.0, due to gross displacement. At the same time, usually the set from a 99 to 101mm bore requires different practices during assembly when it comes to setting oil ring tensions (fish scaling) and etc. I find that when people build their own engines, sticking to a 99mm bore is much more forgiving than going to a 101mm. All too often, the fact that the cylinders are roughly the same price makes people **think** the bigger engine is smarter. It isn't. The bigger engine requires more work to attain efficiency, requires cubic dollars to pay for the cylinder heads, and the engine combination is harder to optimize all around. My 4.3 and 4.4L engines took years to perfect from an efficiency perspective. The 4.4L still isn't perfected when it comes to induction, and camshafts, but the final test engine is being installed next week, so it should be good to sell within a couple of years. The 4.3 grew 40HP in an 18 month period, and is now at 480HP net, but that comes with a ton of work Make all the displacement considerations based on how much you can spend on cylinder head work. At the end of the day, bigger is seldom better, and it never is the first time around. 2-its not about "bang for buck". It's more about less Vs more when it comes to efficiency. The 3.8 loves the stock cams, set straight up. A 4.0 with proper head work can also retain the stock cams, but throw away the factory cam timing tools, and set them up on some split lobe centers, and you'll find efficiency. I have used stock cams in a 4.3L engine, and found 30HP in just playing with the cam timing, and throwing away the factory specs. I will say that ANY playing around with cams instantly requires the ECU to be tuned, else the engine will do nothing well. In some instances it won't even idle. Again, a 3.8 is very forgiving from this perspective, as you can run the stock cams straight up, and have wiggle room. I see too many people trying to build things perfectly the first time, when they have no experience to leverage. The first build needs to be simple. 3- At what point do you go backwards? As soon as you forget about what efficiency is, or as soon as you let the dollars, and timeline make the decision for you concerning what you need. As soon as you start thinking "bigger is better" (and you want to brag to your buddies about how big yours is) you have instantly beaten yourself. Build an engine that can have it's attributes put to use EVERY time that you drive the car. Look for gains in average HP and average Tq. Leave the big peak numbers up to the "bigger is better" crowd, because ll they are going to do is decorate their garage with the car, anyway.

So Jake - what you state above has me concerned. I am going from 3.4 to 3.8 with Nickies from LN. I was assured that this would not be a problem with the stock ECU. My concern was with its ability to keep up with the fuel demands of the larger displacement. I'm sure there's more involved, but that was my immediate concern. The heads will be going to Hoffman for the 996 Spec class treatment. Everything else is expected to be stock. The obvious question: is this a bad strategy? Should I go only to 3.6? I have no plans to do a "tune". I am looking for a sturdy robust engine that I won't have to worry about failing in the foreseeable future. I'll be following all of the precautions I've read from LN, their RND engine program and from your videos. I'll be using all new parts just about everywhere and will carefully follow the break-in recommendations. Is the jump from 3.4 to 3.8 asking for trouble?

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More importantly what are you targeting for compression ratio, and what head work do you plan to do? Again, size isn't the sole determining factor. Further, you will NOT run out of fuel till beyond 500HP with these systems, at around 440HP we run out of injector (with white injectors). The main issue is the ECU needing tuning to keep the engine from over- fueling. This is where you assume the role of engine builder; not engine assembler. The difference is that one bolts things together, and the other one whips the combination into submission, assuming nothing and quantifying everything.

Jake took my 7/98 build from 3.4 to a 3.8 without a tune and it makes me smile every time I drive it.

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Its all in the combo 😎

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I guess I had better start quizzing LN. I may have been making a lot of assumptions. One being the engine will maintain stock compression ratio, with the pistons they provide as part of the Nickies "kit". The head treatment would include pressure testing, valve inspection and grind, "Serdi" seat profiles, R&R guides, back-cut on the intake valves, resurface of the exhaust flange surface, new and cryo-treated valve springs. I am not looking for big power gains. I am looking for a solid engine with improvements to reliability. Gaining a little more output from the displacement increase and the minor head-work, is just a bonus. I'm curious about this over-fueling issue. Why would the ECU not relearn and adapt to the fuel needs based on the feedback received from the O2 sensors? Is this prior to going into closed loop? It seems the beak-in procedure recommended for the RND engine builds, take this very scenario into consideration by warning against allowing the engine to run at idle for the first 15 minutes of run time. Instead, it should be run at 2000 rpm for at least 15-20 minutes. There are several other break-in steps recommended. Many are a bit irregular for "conventional" engines. I'm not expecting this to be conventional. I am expecting it to be a success. I will make every effort to see that it happens.

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The Bosch DME will pull as much fuel as the stock tuning threshold will allow. This is not enough in some cases and the engine is still rich. The tune changes the parameters and targets of the system to pull more fuel. Build it and put it on a dyno , sniffing AFR Before the primary cats and go from there. A tailpipe sniffer will show a leaner mixture, as it is post cat, if you have cats. You can ask all the questions you want. No two engines and fuel systems are the same. Collect data and give the engine what it wants. That will be 13-13.2:1 AFR @WOT

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Thanks for taking the time to assist with this, Jake. Will the fuel trim values collected from a Durametric be helpful in this analysis?

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No. for these tests you�ll not worry about any OBDII data. You�ll collect your own.

That would be a street application.

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OK - so if I understand this, I should have wideband O2 sensors monitoring upstream of the cats. Then what? Change the tune of the DME? I don't see that happening in my garage. My plan is to make the stock DME compensate and adapt to this mildly modified engine. Am I at some great risk with this plan? Let's assume there is no ability to change the tune of the DME. Do you have any suggestions to reduce my risks?

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Unless you have a dyno in the garage, you'll be assuming the tune is ok. There's no place for assumptions, especially with a new engine that has a very small tolerance for over- enrichment during break- in, before the cylinders/ rings glaze. Buy an Innovate Motorsports LM-1 or LM-2. Install this upstream on the cats and drive the car. Try not to get arrested and do some WOT pulls in 3rd gear and see what you have for data. Or, go find a dyno. Ask @dporto about how his car kicked our tail when it came to enrichment. The car "drove fine" and had we not looked for a problem that we didn't know existed, and collected data to analyze, his engine would have already failed, and it would be no fault of the engine, or our work. The rule is that you look for problems that you don't think exist. It's guilty till proven innocent.

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You are spending a ton of money on the build, why not spend some on a tune? Or at least install a wideband and see what the values are, if they are way out of what Jake recommend then do a tune. If they are slightly off then maybe it's ok. That you can do in the garage. 14point7 is the controller I would buy ​​​​​ interesting how the DME makes it to rich, I would think the opposite. Maybe it's something with having a MAF vs MAP

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^^^This is why I paid FSI to "build" my engine^^^ I certainly could have done the assembly work myself - tuning/knowing, not so much! Bringing it to someone who's just looking at #'s without really knowing the engine or what to expect from it is asking for trouble. " Ask dporto about how his car kicked our tail when it came to enrichment." ^^^ It took them close to 2 months to properly diagnose/identify the problem/culprit and then fix and properly tune it (I was supposed to get the car back in mid April 2019 and didn't get it 'til June - as stated in a couple other threads, this condition was unbeknownst to me and was by no fault of FSI - the fact that they found it and fixed it is what makes them worth every penny spent). The engine would go lean on the dyno at around 5500 - 6k rpm. It "ran fine" below that range. It turned out to be the Venturi Tubes in the C4 fuel tank that were causing the problem (cracked tube that would only leak/suck air under extreme high rpm conditions). I highly doubt that if I'd built the engine and brought it to a "Tuner", they would have caught or cared about such a condition. I would have gotten the car back, assumed that everything was good and slowly but surely (I don't drive around at 6k very often) been killing my engine...

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Did the fuel pressure drop? Would be good to have a sensor for that!

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It would not drop, it would only become unstable as the fuel became aerated. The way we finally found it was with an old school mechanical gauge during a dyno pull. A digital instrument would not show the issue, but the mechanical gauge did, as the needle behavior would go erratic right at the same point where the AFR would lean out. The lean condition was not RPM referenced, it was time referenced. The issue would occur at all different RPM points, but would take about 7 minutes of run time before it would happen, due to the aeration level of the fuel needing to occur before the symptom would show up. At first we thought it was a coolant temp communication issue, since the engine would always be about the same temp when the issue would start. Find this one in "Google" during your "research". I laugh every time someone calls me who has been "well- informed" via Google through "research".

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That must have been a difficult thing to find! would this have caused the engine to melt? If you wouldn't have found it, would the knock sensors have saved the engine? ​​​​​

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What is this in response to? Good information. I'll definitely look into this tool. I don't have a dyno in my garage. Unlikely I ever will. I do have a friend that should be able to help. I'd need to disengage the front drive, as I think his dyno is only single axle. Yes - I would have thought the opposite, as well. Will investigate the 14point7 unit. That is strictly for monitoring, correct? And if things are off, a reprogram (flash) would be needed. What sort of recommendations are there for that?

[QUOTE=Scott at Team Harco;16382682]What is this in response to? Originally Posted by [email removed] [img]images/buttons/viewpost.gif[/img] That would be a street application. QUOTE] This was in response to my question to him about his 3.4 to 4.0 engine project car. Based on his signature I was wondering which application he was building it for.

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Got it. A bit of cross-talk going on here. All good.

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Yes, it's purely for monitoring. It somehow tries to measure the fuel to air ratio in the exhaust. There is a few different ones, Jake mentioned Innovative. Total disclaimer: I don't have a 14point7 wideband but I do have a Innovative and it could be better. But both would work for you. I don't know how you would change the ECU programming or what tool is needed for that.

I like the looks of the 14.7 unit. I have preferred the older LM-1 over the newer LM-2 for years due to simplicity and etc. The newer Innovate (LM-2) certainly is not as good as the LM-1.I buy older LM-1s on eBay. I have had one of mine for 15 years, and it's been taped together for the last 10 of those. Still works great.

Yep decisions decisions,, I have kinda come to grips with the $$, in the end if I really look at it,, if the difference is 4 or 5K ,, I have to say to myself,, your 57,, you've spent more on dumber stuff. There is NO financial win, no allusions, I'll need a stated value loss policy on this puppy,, Because I'll be technically upside down when done,, probably worth near 30(With the right day) and I'll be 35+ into the car.. I could dump it as a roller but to get the condition/looks in a new one,, there I am at the same $$ give or take.. So right now its the struggle to really decide on the build and the limits. Its Money, , (at a basic level) Time (I would "like" to have the car running this year.) Result, I want a full rebuild, I'm budgeting some overhead for the "while we are there" items. (Most of which will be picked before we start) Execution who to build it, finding a shop I feel is equipped to do the work, I want the build and tune done in 1 location. so far I have a list ,, I've kinda picked my front runner, and now trying to decide my list of needs vs wants vs Nice to have. Proximity there are cost and logistical advantages ,, they can impact your decision. Scope how much motor do I realistically need? vs want.. they are different #'s See us next week on "As the engine turns".. LOL

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Me too,, I have a LM1 with 2 expansion boxes,, never found a engine I couldn't get wired up to it. Its in that class of does its job well without too much fluff.

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Who's doing the work/tune?

I'm wrestling through this same 3.8 vs 4.0 question for my '03 C4 3.6L rebuild (block is currently on its way to LN to get in the work queue and word on the street is that LN is expanding their in-house capacity, so the wait time is beginning to come down and I shouldn't wait too long before deciding), but I'll confess I'm still a little confused about all the advice given so far: Assuming an daily-driven, street-use-only, otherwise-stock, straight displacement increase using the LN 4.0L kit (with the included matching JE pistons), should head work/cam timing/ECU tuning be considered prerequisite necessities to get an efficient, reliable engine or are most of those mainly needed when you start going down the "track performer"-style route with other enhancements to boost power? I'm not trying to save a buck by skipping tuning or other work, I just feel like I've been getting mixed answers about what I need to do my engine "right" and have something I can trust to not grenade again in the future. Maybe I'm misreading Jake's comments above, but I'm getting the impression from him that I really ought to insist on those items if I go 4.0, whereas others I've talked to feel they're overkill for my build. Any advice? Also, is it true that the general consensus is that going to 4.0 isn't that much of a performance bump over 3.8 anyway?

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I would think that if you just increase displacement without more airflow, you will end up with the same horsepower and more torque. So to get more out of the 400cc increase, you�d probably want to do the head work, and/or make other improvements for airflow.

Don't know about performance boost between the two options but I can tell you I absolutely love my street only 3.8 Stage 1. More than I will ever need or use. Breathtakingly FAST and QUICK!

There's no such thing as overkill. Overkill doesn't exist in engine building. Find new people to ask questions, if you are getting answers like that.

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Haha, in one sense my OCD/perfectionistic tendencies completely agree with you: none of my personal hobby projects are considered "acceptable" unless they are insanely over-engineered and assembled with extreme precision (which is why I now have arguably the most elaborate filtration system ever installed on a 55 gallon aquarium!). On the other hand, even FSI's varying product tiers tacitly acknowledge the reality that not all upgrades make sense for every build. A track-oriented sump might be perfect for a car that'll encounter possible starvation issues on long sweeping turns and certainly wouldn't hurt a street-oriented build, but would still be "overkill" in the sense of not justifying the cubic dollars for a benefit that won't be realized. I think that's where this person was coming from: they read your input in post #17 and thought most of your advice was geared for track-oriented engines with more elaborate upgrades and thus mine wouldn't see the level of benefit to justify them. I have absolutely zero interest in cutting corners on my build, but I also work way too hard for my money to want to spend it where it doesn't make meaningful power/reliability sense or only confers bragging rights ("4.0L because 'Murica!" does nothing for me). Hence my post: trying to figure out what I ought to do for this particular build to do to get it "right."

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That's why you deal with someone who knows what you need, and will provide that, despite what you "want". Its my job to understand the application, and to differentiate between what you want, and what you need. We receive pages of input as worksheets, so we can determine how the car is already set up, and record what the applications will be. This helps us make sure that what is being proposed is really what is needed, and I don't just use their answers to determine this, I use the way the answers are formulated to determine this. It also helps me determine if they have unreasonable expectations that we can/ cannot meet. The purchaser didn't design the engines, or engine program, and they don't understand the differences in what the engines are intended to do. That's not their job, its my job. This goes further than bolt on items, which we put very little emphasis on. When you refer to my varying tiers of engines, understand that no compromise is made for a Stage I engine, just because it is a Stage I. The things that separate Stage 1 and Stage II engine are mostly cylinder head port work, compression ratio, and cam timing specs. The Stage I engine will not see track time, so it doesn't get billet connecting rods, but it does get ARP connecting rod bolts. It has a smaller bore size, which can't handle the larger ports, and due to that the compression ratio doesn't provide any benefits if we go higher than stock. Look at this from the Stage I being built as overkill for the street, and Stage II as overkill for the track, but not really... Because overkill doesn't exist. :-) The Stage III is so over built that seldom can anyone afford it, and fewer people even need it. We usually build 3-4 of those per year, and that's it. This is one of my questions that potential purchasers fill in on my "Gauntlet Worksheet". It asks very directly why the engine is being purchased, and one of the multiple choice selections is "to impress my buddies". Someone that checks that box is going to get an additional phone call from me before I accept the project, without a doubt. I don't play that game, and its a really quick way to deal with the wrong person, with the wrong intentions, who can't be pleased, and is impatient.

I chose the stage 1, it made the most sense for my application.

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I agreed.. Living in Hawaii you'd never have a need for a Stage II. You passed my "Gauntlet" with flying colors. Can't say the same for another guy from last week :-)

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You will LOVE it! Trust me... I'm an old guy and my days of tearing up the track and getting speeding tickets on the streets are over(hopefully). As I said before my Stage 1 is night and day different from my pre-reconstructed engine. It gives more than I could ever ask for street operation. Smooth deceptive power and a sound above 3,000rpm you probably haven't heard with your current engine. I will tell you that it requires a cranial recalibration of actual speed. The first few times I drove the Stage 1 I was consistently above the posted speed limits not because I was leaning on it(I did that too and it is amazing) but because the power is so deceptive. You made an excellent choice IMHO.

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^^^ Nah... get the stage II Just kidding - You'll be knocked out either way I plan on doing some auto x and maybe a couple HPDE's this year, so I felt like I "needed" (whatever that means...) the extras - which are mighty impressive btw (have I said that before?).

The hardest part of a street engine build is deciding on the cut-off,, a race engine is much easier, your usually limited to what you can do (rules) and there isnt a real limit to what you can use.. Its racing.. LOL The 850 HP sprint car I play with,, the engine would suck on the street.. well would suck most of the time.. You get a lot of power in a very short amount of throttle.. of course it weighs about 1/2 a 911

Not had time to digest this whole post but advice given seems really good and comprehensive. If anyone is interested in a long technical read about the benefits of increased capacity and alternative builds you can obtain a free copy of our report on oversized engines from [email removed] Don't please complain that it has a lot of detail - I have warned you and you don't have to read it! We also manufacture deep valve racing sumps, Accusump adapters and numerous other racing components for those interested in track use. Off to our first second test on Sunday of our Cayman S fitted with a new type of oil delivery from t he Accusump after extensive tests and issues and keeping gingers crossed over the outcome. Problem is it looks like showers all day - so "G" forces might be down but at least it relieves the winter boredom! Baz.